1. Field of the Invention
The present invention relates to a motion controller and a system identifying method for accurately estimating inertia, viscous friction coefficient and constant disturbance of an control object (i.e., an object to be controlled).
2. Description of Related Art
In a conventional apparatus for estimating inertia of a motor, estimation of the inertia is performed by integrating a torque command value and a model torque command value within a certain time period and multiplying the ratio thereof by an inertia nominal value, while increasing the precision by eliminating constant disturbance, such as, e.g., viscous friction, Coulomb friction and gravity, using specific operations (see, e.g., WO96/37039).
In FIG. 9, the reference numeral “3” denotes an electric motor, “4” denotes a machine connected to the electric motor 3. A detector 5 is attached to the electric motor 3. The reference numeral “71” denotes a command generator configured to output an operation speed command Vref for the motor. The reference numeral “72” denotes a speed controller which performs proportional-integral control so that the command and the motor speed coincide and outputs a torque command value Tref. The reference numeral “75” denotes a current controller configured to output a current value I so that the motor is operated according to the torque command value Tref. The reference numeral “73” denotes an estimator having a model of the motor. This estimator 73 performs proportional-integral control so that the command and the speed of the model coincide and outputs a torque command Tref′ of the model. The reference numeral “74” is an identifier configured to obtain an inertia estimate value by integrating the actual torque command Tref, the torque command Tref′ inputted in a model at the estimator 73 at the time zone [a, b] and multiplying the ratio thereof by a nominal value J′ of the inertia. In this method, in cases where no disturbance exists, the inertia estimate value coincides with an actual inertial J theoretically.
In cases where, however, constant turbulence, such as, e.g., viscous friction, Coulomb friction and/or gravity exists, constrained conditions for preventing influences of viscous friction and/or Coulomb friction on the integrated value of the torque command value Tref at the time zone [a, b] will be required. Furthermore, in order to eliminate constant disturbance such as gravity, a special innovation will be required.
In WO96/37039, the operations shown in FIG. 10 are used as constrained conditions.
FIG. 10 shows graphs in which the horizontal axis shows a time and the vertical axis shows a speed. Each case satisfies constrained conditions of the following operations.
(Constrained conditions of an operation for eliminating viscous friction and Coulomb friction) The integrated values of the speed Vfb in the zone [a, b] is zero. This is represented by, e.g., reciprocating movements.
(Constrained conditions of an operation for eliminating constant disturbance) Inertia J1 obtained from the zone [a1, b1] when operated by a certain speed command and inertia J2 obtained from the zone [a2, b2] when operated by a reverse command in which the positive and the negative are reversed are obtained, and then the average value of J1 and J2 is obtained.
As explained above, in a conventional control constant identifier, inertia J was identified by making an operation satisfying the above explained operation constrained conditions.
In a conventional inertia estimator, because of the aforementioned two constrained conditions, influence of constant disturbance, such as, e.g., viscous friction, Coulomb friction and gravity, could not be eliminated by a single positioning operation or the like, resulting in failure of inertia estimation.
Furthermore, if inertia is identified by ignoring the constrained conditions, there is a problem that the inertia estimation errors increase.